Structural Features of Lead Iron Phosphate Glasses

Lead iron-phosphate glasses were investigated for use as wasteform because of their improved chemical durability. There is a controversy if lead should or should not be used in iron phosphate glasses, and on the role of Fe in the inhibition of corrosion. The structure of the 43.3PbO·13.7Fe2O3·43P2O5 (mol%) glass, which has a dissolution rate in aqueous solution at 90 °C of 1.26×10−9 g/cm−2 min−1, and the same O/P ratio, 3.5, as the lead-free 40Fe2O3·60P2O5 glass, was investigated. Glass samples were produced by melting batches of Fe2O3, PbO, and NH4H2PO4 at 1100 °C for 1 h, and pouring the liquid into steel mold. Samples were annealed at 450 °C for 3 h. Some samples were crystallized by heating at 700 °C for 24 h. X-ray diffraction, Mössbauer, EPR, infrared, and Raman scattering spectroscopy were performed and compared to spectra obtained after crystallization. The crystalline phase Fe2Pb(P2O7)2 was identified after crystallization. The hyperfine parameters from the Mössbauer spectrum indicates that Fe2+ and Fe3+ ions are in octahedral coordination, and some of the Fe3+ ions in the starting batch are reduced to Fe2+ ions after melting. The infrared and Raman scattering spectra are representative of a mixture of chain-terminating Q1 species and chain-forming Q2 species. No Raman bands related to P=O vibrations and Q0 species were observed. From the EPR measurements it is concluded that all Fe3+ ions are not constrained to central positions of tetrahedral and octahedral sites of the glass formers